This application is based on and claims priority to Japanese Patent Application No. 2001-223982, filed Jul. 25, 2001, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention generally relates to a four-cycle engine for a marine drive, and more particularly to a four-cycle engine for a marine drive that has a vertically extending camshaft.
2. Description of Related Art
Marine drives such as an outboard motors include a marine propulsion device powered by an engine. The propulsion device typically is a propeller and is submerged when an associated watercraft rests on a body of water. The outboard motor can employ either a two-cycle engine or a four-cycle engine. Recently, however, many outboard motors have been offered with four-cycle engines because they provide better emissions control.
Typically, a four-cycle engine includes one or more intake and exhaust valves moving between an open position and a closed position within a cylinder head member. One or more camshafts can be provided to actuate the valves in a timed manner. When the intake valves are open, air is introduced into combustion chambers of the engine through the intake ports. When the exhaust valves are open, exhaust gases are discharged from the combustion chambers through the exhaust ports.
The camshafts typically extend vertically within the engine of an outboard motor. The camshafts are driven by a crankshaft of the engine which also extends vertically. The camshafts and the crankshaft can be provided with sprockets or pulleys around which a timing chain or belt is wound so that the crankshaft drives the camshafts through the timing chain or belt.
The camshafts can be disposed within a single camshaft chamber or separate camshaft chambers. A camshaft cover member or members together with the cylinder head member define the chamber or chambers. Normally, some lubricant oil collects in the camshaft chambers after lubricating other engine portions.
During certain maintenance and repair procedures, the sprockets or pulleys need to be removed from the camshafts and then re-attached afterwards. However, during such procedures, the camshafts should be prevented from rotating. Thus, the camshaft cover member typically is disconnected from the cylinder head member so a tool can be connected to the camshaft so as to prevent rotation thereof. Accordingly, the oil within the camshaft chambers can spill out when the covers are removed, and thereby stain the engine. Thus, the repairperson should pay special attention not to stain the engine with the oil.
Additionally, in some arrangements, the camshaft cover member can be nested in a space defined between the sprocket or pulley and the camshaft so as to shorten the outboard motor in height. If the camshaft cover member is necessary to be removed in this arrangement, the sprocket or pulley should be disassembled first. The camshaft is required not to rotate for the disassembling service of the sprocket or pulley. For instance, the timing chain or belt can be fixed by a certain tool so that the camshaft does not rotate. However, the service is extremely difficult because the outboard motor can only afford a limited space for the service.
A need therefore exists for an improved four-cycle engine for a marine drive that can provide good serviceability of a camshaft and/or components around the camshaft.
In accordance with one aspect of the present invention, an internal combustion engine for a marine drive comprises an engine body. A movable member is movable relative to the engine body. The engine body and the movable member together define a combustion chamber. The engine body defines intake and exhaust ports communicating with the combustion chamber. An air induction system communicates with the combustion chamber through the intake port. An exhaust system communicates with the combustion chamber through the exhaust port. An intake valve is arranged to move between an open position and a closed position. An exhaust valve is arranged to move between an open position and a closed position. A camshaft is configured to actuate either the intake valve or the exhaust valve. The camshaft extends generally vertically. A member is arranged to enclose the camshaft together with the engine body. The member defines an opening through which a tool is capable to pass. The tool is adapted to prevent the camshaft from rotating.
In accordance with another aspect of the present invention, a marine drive comprises an internal combustion engine. A cowling assembly is configured to surround the engine. The engine comprises an engine body. A movable member is movable relative to the engine body. The engine body and the movable member together define a combustion chamber. The engine body defines intake and exhaust ports communicating with the combustion chamber. An air induction system communicates with the combustion chamber through the intake port. An exhaust system communicates with the combustion chamber through the exhaust port. An intake valve is arranged to move between an open position and a closed position. An exhaust valve is arranged to move between an open position and a closed position. A camshaft is configured to actuate either the intake valve or the exhaust valve. The camshaft extends generally vertically. A member is arranged to enclose the camshaft together with the engine body. The member defines an opening. The cowling assembly comprises top and bottom cowling members. The top cowling member is detachably coupled with the bottom cowling member. The opening is disposed above a top end of the bottom cowling member.